Methods and apparatus for home node-b detection and measurements thereof

ABSTRACT

A method and apparatus for selecting or reselecting a home Node-B (HNB), (i.e., a closed subscriber group (CSG) cell), among cells having colliding physical layer signals are disclosed. Once the identity (ID) of an HNB is determined, measurements needed to support cell selection or reselection are performed. A broadcast channel that broadcasts an HNB ID is detected and synchronized to, and information obtained from the broadcast channel is forwarded to a non-access stratum (NAS). The broadcasted HNB ID is checked against an HNB white-list provided by the NAS to determine whether the HNB is suitable for a wireless transmit/receive unit (WTRU). The WTRU selects the HNB to camp on, or changes from a cell currently serving the WTRU to the HNB if it is determined to be more suitable than the current serving cell.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.12/339,395 filed Dec. 19, 2008 which claims the benefit of U.S.Provisional Application No. 61/018,580 filed Jan. 2, 2008, which isincorporated by reference as if fully set forth.

FIELD OF DISCLOSURE

This application is related to wireless communications.

BACKGROUND

Efforts are currently being made for the Third Generation PartnershipProject (3GPP) long term evolution (LTE) program to introduce newtechnology, new architecture and new LTE settings and configurations inorder to provide improved spectral efficiency, reduced latency, andimproved utilization of radio resources to provide faster userexperiences and richer applications and services at a lower cost.

As part of these efforts, the 3GPP LTE program is working on introducingthe concept of a home evolved Node-B (HNB) in LTE, (and also, possiblyin a parallel fashion, in Release 8 wideband code division multipleaccess (WCDMA), global system for mobile communications (GSM) enhanceddata rates for GSM evolution (EDGE) radio access network (GERAN) andother cellular standards). The HNB is intended to be similar to awireless local area network (WLAN) access point (AP), and is to bedesigned in a manner that allows access to cellular services to usersover extremely small service areas, (e.g., homes or small offices). Thiscan be particularly useful in areas where cellular networks have notbeen deployed and/or legacy radio access technology (RAT) coverageexists, as well as in areas where cellular coverage may be faint ornon-existent for radio related reasons, (e.g., an underground metro orshopping mall). The subscriber, (e.g., an individual or anorganization), may deploy an HNB over an area where such service isdesired.

An HNB in an LTE network may be identified by means of a unique trackingarea (TA) identity (ID), cell ID, or a combination of both. The problemthat may be encountered with this approach is that in order to read theID of a cell, a wireless transmit/receive unit (WTRU) has to acquire thecell broadcast information of the HNB. However, when the WTRU is in aconnected mode while performing measurements, the WTRU does not usuallyread the radio resource control (RRC) layer broadcast channel. However,if the WTRU were to do so, it might lead to unacceptable performancerequirements since there may be many HNBs in the vicinity.

One possible solution is that HNBs be identified at the physical (PHY)layer by means of a reserved physical layer synchronization signal. InLTE, there are three possible primary synchronization channels (P-SCH)and 170 possible secondary synchronization channels (S-SCH), for a totalof 510 unique physical layer cell IDs. However, a problem with thissolution is that the PHY layer cell ID of two or more HNBs may collide,and the WTRU may not be able to distinguish between them.

In earlier systems, cell planning techniques were sufficient to ensurethat there was no collision between neighboring cells of differentoperators. However, with potentially hundreds of HNBs in the vicinity ofthe WTRU, (belonging to potentially multiple operators), cell planningtechniques may be less effective. In such a scenario, it becomesnecessary to address the issue of WTRU procedures when a collisionbetween neighboring cells is detected.

SUMMARY

A method and apparatus for selecting or reselecting an HNB, (i.e., aclosed subscriber group (CSG) cell), among cells having collidingphysical layer signals are disclosed. Once the identity (ID) of an HNBis determined, measurements needed to support cell selection orreselection are performed. A broadcast channel that broadcasts an HNB IDis detected and synchronized to, and information obtained from thebroadcast channel is forwarded to a non-access stratum (NAS). Thebroadcasted HNB ID is checked against an HNB white-list provided by theNAS to determine whether the HNB is suitable for a WTRU to camp on. TheWTRU selects the HNB to camp on, or changes from a cell currentlyserving the WTRU to the HNB if it is determined to be more suitable thanthe current serving cell.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example and to be understood in conjunction with theaccompanying drawings wherein:

FIG. 1 shows a WTRU in communication with a cell that potentially may besuitable for the WTRU to camp on; and

FIG. 2 is a flow diagram of a procedure for selecting or reselecting anHNB among colliding cells.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment.

When referred to hereafter, the terminology “base station” includes butis not limited to a Node-B, an evolved or E-UTRAN Node-B (eNodeB), asite controller, an access point (AP), or any other type of interfacingdevice capable of operating in a wireless environment.

Hereafter, the terms home Node-B (HNB) and closed subscriber group (CSG)are equivalent. Although this application describes features from theperspective of collision detection and resolution of HNB physical (PHY)layer IDs, they are applicable to the collision detection and resolutionof any cells (e.g., macrocells). These concepts are applicable tovarious wireless standards, such as WCDMA, GSM, IEEE 802.16 wirelessmetropolitan area networks (WiMAX), and the like.

The white-list of HNBs that the network configures the WTRU with mayinclude the PHY layer ID of the HNB to which the WTRU has access, suchas a primary synchronization channel (P-SCH), a secondarysynchronization channel (S-SCH), some other ID, or a combinationthereof. Additionally, the white-list includes any upper layer ID ofthose HNBs, such as a tracking area (TA) ID, a cell ID, a CSG ID, someother ID or a combination thereof. This PHY layer ID may belong to oneof many reserved for HNB access. A WTRU that detects a P-SCH/S-SCH whichbelongs to this reserved list would know immediately that it hasdetected an HNB. Certain physical layer IDs are reserved for “public”HNBs and others are reserved for “private” HNBs.

When a cell has been determined by the WTRU to be an HNB, layer 1 (i.e.,a PHY layer) of an access stratum (AS) in the WTRU forwards relevantbroadcast information, (e.g., management information field (MIB), SU-1,or the like), received from the cell to upper layers (i.e., layer 2/3)in the AS, as well as to a non-access stratum (NAS) in the WTRU. Forexample, a primitive may be used to indicate that the cell is an HNB.Optionally, the PHY layer may distinguish if the HNB is a “public” HNBor a “private” HNB to the upper layers.

The function of the AS is to support the NAS. This includes thefunctions and protocols for the transport of information across theUTRAN and air interface. The NAS is responsible for different aspectslike call control, mobility management, session management and the like.

An additional identification of the HNB may be carried on the downlinkphysical channels of the HNB, such as by allocating a few bits that maybe carried on any physical channel, (e.g., physical broadcast channel(P-BCH), common control physical channel (CCPCH)). This additionalidentification of the HNB may also be configured in the WTRU as part ofits white-list, and may be used by the WTRU to resolve a collision incase it detects a collision in the P-SCH/S-SCH.

When the WTRU is in an idle mode, as part of a cellselection/reselection procedure, and the WTRU detects multiple instancesof the PHY layer HNB IDs that the WTRU has access to, (e.g., using awhite-list), the WTRU may perform any or all of the following in anycombination.

The WTRU may provide an indication of the collision to upper layers,(e.g., radio resource controller (RRC)), and optionally provide anindication to the upper layers about the scale of the collision (e.g.,three identical signals are detected).

For each of the PHY layer IDs, the WTRU may proceed to make measurementson a reference symbol, acquire at least one broadcast channel and passthis information to the upper layers. The upper layers may resolve thecollision by checking the upper layer identification of the HNBs, (e.g.,TA ID, CSG ID, cell ID, some other ID or combination of the above). Ifthe HNB meets the criteria for cell selection/reselection, which may bedetermined by the measurements and access parameters, then the upperlayers may pass the information about the selected HNB back to the PHYlayer to allow the PHY layer to perform its own procedures for campingon the particular cell. For this purpose, the PHY layer may maintain anordered list or memorize the order of the collision.

In addition, the upper layers may instruct layer 1 as to how manybroadcast channels to acquire, and/or how many measurements to make(e.g., acquire the x strongest of the y cells for which collision isdetected, where x≦y).

Optionally, the above procedures may only be performed by the layer 1and upper layers for the cells for which collision is detected and meetsome other criteria, (e.g., some basic radio related criteria such ascell selection criteria S or equivalent for HNBs). Use of any additionalidentification of the HNB that may be carried on the downlink physicalchannels of the HNB to resolve the collision

When the WTRU is in a connected mode, and the WTRU detects multipleinstances of the PHY layer HNB ID that belong to the list of cell IDs ofinterest and the WTRU has access to, (e.g., using white-list), the WTRUmay perform any or all of the following in any combination.

The WTRU may provide an indication of the collision to upper layers andoptionally provide an indication to the upper layers about the scale ofthe collision, (e.g., three identical signals are detected). For each ofthe PHY layer IDs, the WTRU proceeds to make measurements on a referencesymbol and acquire the broadcast channels and pass this information toupper layers. The upper layers may resolve the collision by checking theupper layer identification of the HNBs, (e.g., TA ID, CSG ID, cell ID,some other ID or combination thereof). The upper layers may report themeasurements of only those cells which it has access to. The upperlayers may pass the information about the selected HNB back to the PHYlayer to allow the PHY layer to “remember” the particular cell in caseof a future handover. For this purpose, the PHY layer may maintain anordered list or memorize the order of the collision.

The upper layer (e.g., RRC) may instruct the PHY layer of how manybroadcast channels to acquire and/or how many measurements to make(e.g., acquire the x strongest of the y cells for which collision isdetected where x≦y).

Optionally, the above procedures may only be performed by the PHY andupper layers for the cells for which collision is detected and meet somecriteria (e.g., some basic radio related criteria such as cell selectioncriteria S or equivalent for HNBs). The upper layers may provide anindication to the network, (e.g., in the measurement report) that acollision was detected. Any additional parameters such as the scale ofthe collision, (e.g., three identical signals are detected), may beprovided. The network may use this information to configure a longermeasurement gap which may allow the WTRU to resolve the collision,(e.g., by checking upper layer identification of the HNB). The networkmay instruct the WTRU to move to idle mode and then select the cell.This command may be implemented either immediately or at a futureinstance of time as indicated by the network (e.g., transmission timingintervals (TTIs), system frame numbers (SFNs)).

The WTRU may use any additional identification of the HNB that may becarried on the downlink physical channels of the HNB to resolve thecollision.

FIG. 1 shows a WTRU 100 in communication with a cell 105 thatpotentially may be suitable for the WTRU to camp on. The WTRU mayinclude an antenna 110, an AS 115 and a NAS 120. The AS 115 may includeupper layers 125 (layer 2/3) and a PHY layer 130 (layer 1).

FIG. 2 is a flow diagram of a procedure 200 for selecting or reselectingan HNB among colliding cells. Referring to FIGS. 1 and 2, in step 205,the NAS 120 in the WTRU 100 is configured to include a white-list ofHNBs (i.e., CSGs). In step 210, the WTRU 100 determines the ID of a cell105 in accordance with a P-SCH 135 and an S-SCH 140 associated with thecell 105. In step 215, a determination is made as to whether the cell isan HNB (i.e., CSG cell). If the cell 105 is not an HNB, the procedure200 terminates. If the cell 105 is an HNB, the WTRU 100 performsmeasurements needed to support cell selection or reselection (e.g.,performs measurements on a reference symbol) in step 220. In step 225,the WTRU 100 acquires (i.e., detects and synchronizes to) at least onebroadcast channel 145 that broadcasts an HNB ID. In step 230, the AS 115in the WTRU 100 receives broadcast information from the acquiredbroadcast channel and forwards relevant broadcast information to the NAS120. In step 235, the NAS 120 provides the HNB white-list to the AS 115.In step 240, the upper layers 125 (i.e., layer 2/3) of the AS check thebroadcasted HNB ID against the HNB white-list provided by the NAS 120.In step 245, a determination is made as to whether the cell 105 issuitable for the WTRU 100 to camp on. If the cell 105 is not suitable,the procedure 200 terminates. If the cell 105 is suitable, the upperlayers 125 of the AS 115 pass information about the suitable cell to thephysical layer 130 of the AS 115 (step 250). Finally, in step 255, thephysical layer 130 of the AS 115 performs a cell selection orreselection procedure. If a cell selection procedure is performed, theWTRU 100 selects the suitable cell to camp on. If a cell reselectionprocedure is performed, the WTRU 100 changes a cell that is currentlyserving the WTRU 100 to the suitable cell if the suitable cell isdetermined to be more suitable than the cell that is currently servingthe WTRU.

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB)module.

What is claimed is:
 1. A method of reselecting a closed subscriber group(CSG) among cells having colliding physical layer signals, the methodcomprising: performing measurements needed to support cell reselection;detecting and synchronizing to a broadcast channel that broadcasts a CSGcell identity (ID); forwarding information obtained from the broadcastchannel to a non-access stratum (NAS); checking the broadcasted CSG cellID against a CSG white-list provided by the NAS to determine whether theCSG cell is suitable for a wireless transmit/receive unit (WTRU); andthe WTRU changing a cell that is currently serving the WTRU to the CSGcell if the CSG cell is determined to be more suitable than the cellthat is currently serving the WTRU.
 2. The method of claim 1 wherein theCSG cell ID is determined in accordance with a primary synchronizationchannel (P-SCH) and a secondary synchronization channel (S-SCH)associated with the CSG cell.
 3. The method of claim 1 wherein themeasurements performed to support cell reselection include measurementsperformed on a reference symbol.
 4. The method of claim 1 wherein anaccess stratum (AS) uses the white-list provided by the NAS to determinewhether the CSG cell is suitable for the WTRU.
 5. The method of claim 4further comprising: upper layers of the AS passing information about thesuitable CSG cell to a physical layer of the AS; and a physical layer ofthe AS performing a cell reselection procedure to change from thecurrent cell to the CSG cell.
 6. A wireless transmit/receive unit (WTRU)for reselecting a closed subscriber group (CSG) cell among collidingcells, the WTRU comprising: an access stratum (AS); and a non-accessstratum (NAS), wherein the WTRU is configured to: perform measurementsneeded to support cell reselection; detect and synchronize to abroadcast channel that broadcasts a CSG cell identity (ID); forwardinformation obtained from the broadcast channel to the NAS; check thebroadcasted CSG cell ID against a CSG white-list provided by the NAS todetermine whether the CSG cell is suitable for the WTRU to camp on; andchange from a cell that is currently serving the WTRU to the CSG cell ifthe CSG cell is determined to be more suitable than the cell that iscurrently serving the WTRU.
 7. The WTRU of claim 6 wherein the CSG cellID is determined in accordance with a primary synchronization channel(P-SCH) and a secondary synchronization channel (S-SCH) associated withthe CSG cell.
 8. The WTRU of claim 6 wherein the measurements performedto support cell selection or reselection include measurements performedon a reference symbol.
 9. The WTRU of claim 6 wherein the AS uses thewhite-list provided by the NAS to determine whether the CSG cell issuitable for the WTRU.
 10. The WTRU of claim 9 wherein the AS comprisesupper layers and a physical layer, wherein the upper layers areconfigured to pass information about the suitable CSG cell to a physicallayer of the AS, and the lower layer is configured to perform a cellreselection procedure to change from the current cell to the CSG cell.11. A method of selecting a closed subscriber group (CSG) among cellshaving colliding physical layer signals, the method comprising:performing measurements needed to support cell selection; detecting andsynchronizing to a broadcast channel that broadcasts a CSG cell identity(ID); forwarding information obtained from the broadcast channel to anon-access stratum (NAS); checking the broadcasted CSG cell ID against aCSG white-list provided by the NAS to determine whether the CSG cell issuitable for a wireless transmit/receive unit (WTRU); and the WTRUselecting the CSG cell to camp on if it is determined to be suitable.12. The method of claim 11 wherein the CSG cell ID is determined inaccordance with a primary synchronization channel (P-SCH) and asecondary synchronization channel (S-SCH) associated with the CSG cell.13. The method of claim 11 wherein the measurements performed to supportcell reselection include measurements performed on a reference symbol.14. The method of claim 11 wherein an access stratum (AS) uses thewhite-list provided by the NAS to determine whether the CSG cell issuitable for the WTRU.
 15. The method of claim 14 further comprising:upper layers of the AS passing information about the suitable CSG cellto a physical layer of the AS; and a physical layer of the AS performinga cell reselection procedure to change from the current cell to the CSGcell.
 16. A wireless transmit/receive unit (WTRU) for selecting a closedsubscriber group (CSG) cell among colliding cells, the WTRU comprising:an access stratum (AS); and a non-access stratum (NAS), wherein the WTRUis configured to: perform measurements needed to support cell selection;detect and synchronize to a broadcast channel that broadcasts a CSG cellidentity (ID); forward information obtained from the broadcast channelto the NAS; check the broadcasted CSG cell ID against a CSG white-listprovided by the NAS to determine whether the CSG cell is suitable forthe WTRU; and select the CSG cell to camp on if it is determined to besuitable.
 17. The WTRU of claim 16 wherein the CSG cell ID is determinedin accordance with a primary synchronization channel (P-SCH) and asecondary synchronization channel (S-SCH) associated with the CSG cell.18. The WTRU of claim 16 wherein the measurements performed to supportcell selection or reselection include measurements performed on areference symbol.
 19. The WTRU of claim 16 wherein the AS uses thewhite-list provided by the NAS to determine whether the CSG cell issuitable for the WTRU.
 20. The WTRU of claim 19 wherein the AS comprisesupper layers and a physical layer, wherein the upper layers areconfigured to pass information about the suitable CSG cell to a physicallayer of the AS, and the lower layer is configured to perform a cellreselection procedure to change from the current cell to the CSG cell.